The purpose of this project is to study the relationship between the distribution of methyl mercury in the cochlear fluids and the alteration of the cochlear potentials in guinea pigs. Animals are treated with methyl mercury chloride labeled with C14 and/or Hg203. Radioactivity in the endolymph, perilymph, cerebrospinal fluid and whole blood is measured with a liquid scintillation counter. The stimulus-related responses as well as the DC polarization of the endolymph are recorded from the cochlea. The cochlear microphonic and action potential are suppressed by methyl mercury but the endolymphatic potential remains unchanged. No specific accumulation of the methyl mercury is found in either the perilymph or endolymph.